For both of those reasons, it's an insane idea. But if you really look into his positions, it's even crazier. This article explains how Johnson is even worse than Trump:
If all you’ve done is watched a few clips of Gary Johnson on the internet, it’s easy to be taken in. He knows how to talk like he wants to stand with ordinary folks against those big corporate interests. But Donald Trump does that too, and he doesn’t mean it either. Gary Johnson is a deceitful person who sells himself as Bernie Sanders lite while in reality he has consistently supported a far right agenda that would devastate the country. He hawks his liberal positions on social issues while concealing a deeply disturbing and malicious economic agenda. More than anyone else running, he knows how to put lipstick on the pig that is the Libertarian Party
I'm not going to go into the details. You can read them here, if you want, although the fact that he's a Libertarian should tell you all you really need to know. No one is more faith-based than Libertarians. They tend to follow their beloved philosophy to its most absurd conclusions.
And I certainly don't have a big problem with Hillary Clinton. She's more conservative than I'd like, but most people are. And she's certainly capable and knowledgeable, well-prepared to be our next President of the United States.
It should be a slam-dunk. But there are crazy people on both sides of the political spectrum (most on the right, but not all). Even worse, there are stupid people, ignorant people, gullible people. A democracy is only as good as its citizens. Are we Americans capable of sustaining our democracy? I guess we'll see in a few months, huh?